1. Field of the Invention
This invention relates to using elastic interface spare bus wires and particularly to support them for manufacture and support in the field by ensuring proper testing of the spare nets and a means to record the nets to repair on the module that are accessible by the service structure for the system.
2. Description of Background
The IBM Corporation for many generations has used glass ceramic interconnection modules in its manufacture and design of large computer systems. These modules have many layers of connections in them and are used to provide bus connections from chip to chip and from the chips to the hoards and cards they are connected to. These modules contain many multi-bit wide buses between the various chips mounted on them. In the past when there was a manufacturing defect in the connections in the module there were two choices. It could be re-worked and the defect wire could be re-routed near the surface of the module. This requires a unique fix for every module wire failure. There are limits to how many and which net connections could be fixed in this way. The other choice was to scrap the module as unfixable. In recent generations IBM has been using the Elastic Interface first patented as U.S. Pat. No. 6,334,163 published Dec. 25, 2001 wherein an elastic interface apparatus and method is implemented.
An Elastic Interface (EI bus connections) can be generalized in that these are bus connections which are high speed interfaces that have clock sent with data. All of the data bits are aligned to the clock to be able to latch the data at these high speeds. It requires that the net topology and timing characteristics for each net on the bus are at least similar to each other in order to make it possible to line up the edges of the data to the clock. In this environment re-working connections in the connection module were not easily possible due to the fact that all the nets had to have similar topology and timing characteristics. This increased the difficulty of a re-work solution or made it impossible. This increased the modules that needed to be scrapped as not usable.
The advent of Elastic Interface repair (such as shown in IBM assigned US Patent application number US 2004/0136319 A1, filed Jan. 9, 2003 incorporated herein by reference) introduced the concept of a spare wire built in the bus interface in the connection module that had the same topology and characteristics of the rest of the nets in the bus. It includes the hardware to be able to switch from the bad net in the interface to the spare net. However this operation must now be supported from original manufacture and through out to the customer use in the field. The connection module is tested at several different process corners such as low and high temperature, low and high voltages are good examples of some of these process corners. When a net on the interface is known to be bad the spare net should be used on the bus for testing and the known bad net should not be tested. When the bus does not have a defect the spare net needs to be tested in addition to all the functional nets. In the original design specification for the EI spare not it was driven with a constant zero when not used.
The machine service structure must be able to obtain the information about what nets to repair and be able to apply that repair each time the machine is powered on. It also must be easy to apply as it must be done to both sides of the repaired bus. This recording of which nets are bad and require spare net repair actions must be done after the chips have been mounted on the module.